It is a customary practice in the vacuum cleaner industry to provide a powered rotary brush having rows of stiff bristles for loosening and helping to pick up dirt and other debris. The rotary brush is generally driven by the impeller motor through a flexible drive belt. Necessarily, the impeller motor is quite powerful in relation to the power required for driving the brush roller and it runs at a fairly high rate of speed necessitating a very small diameter driving pulley and a relatively large driven pulley. With this construction should the rotary brush become stalled or its speed of rotation reduced, the drive belt will then slip on the small drive pulley resulting in overheating of the belt and possible damage thereto.
There are relatively sophisticated electromagnetic or electronic devices in use today for recognizing the malfunction and cutting off power to the motor or decoupling the roller from the drive motor. See for example U.S. Pat. No. 4,099,291, July 11, 1978, Bowerman which discloses a vacuum cleaner having a torque limiting magnetic drive device, the input side of which is driven directly by the fan motor, and the output side of which drives the brush roller. This magnetic drive is supported independent of the brush roller, transmitting its driving force thereto through a drive belt. The purpose of the device is to prevent damage should the brush roller stall or become overloaded. In addition, see U.S. Pat. No. 4,163,999, Aug. 7, 1979, Eaton et al which is assigned to the assignee of the present invention and the teachings of which are incorporated herein by reference. Eaton discloses an upright vacuum cleaner having a powered brush roller of the type described above and a Hall Effect device for measuring the rotational speed of the brush roller. When that speed falls below some predetermined minimum level, the power to the motor is automatically shut off thereby preventing damage to the belt.
In both Bowerman and Eaton there is no provision for a signal to the operator warning of the malfunction. Thus, the operator may not be immediately aware of the reduced performance of the vacuum cleaner. Additionally, both these constructions employ rather sophisticated electronic or electromechanical devices. The present invention overcomes these difficulties by the use of a relatively simple mechanical device.
The above citations comprise what the applicant believes to be the closest art of which he is aware that is relevant to the examination of this application.